JP2023544088A - Electrostatic micropump and process of manufacturing electrostatic micropump - Google Patents

Abstract

One embodiment according to the invention is an electrostatic micropump comprising a diaphragm device including a diaphragm and a first electrode structure. The electrostatic micropump further includes a valve device including an inlet check valve and an outlet check valve, the diaphragm device and the valve device at least partially surrounding the pump chamber. The electrostatic micropump further includes a second electrode structure arranged to form an electrostatic drive with the first electrode structure. The electrostatic actuator is configured to deflect the diaphragm. The electrostatic micropump further comprises at least one anti-stiction bump disposed between the first electrode structure and the second electrode structure, wherein in the non-operating state of the micropump, the first electrode structure The spacing between the body and the second electrode structure varies from a peripheral region of the pump chamber towards a central region of the pump chamber, the peripheral region surrounding the central region. [Selection diagram] Figure 2

Description

Embodiments according to the invention relate to micromechanical actuators. Further embodiments according to the invention relate to micromechanical pumps. Further embodiments according to the invention relate to electrostatic micromechanical pumps.

Vertical electrostatic actuators exhibit instability during operation because the electrostatic forces above the characteristic voltage exceed the hydrostatic pressure of the electrode spacing and mechanical restoring forces. If the non-working distance of the electrodes is adjusted, this non-linearity is exploited in the operation of the actuator, lowering the operating voltage and using less energy. Furthermore, operation of electrostatic actuators always requires passivation or insulation of the electrodes and/or sidewalls in the electric field to prevent electrical shorts and even electrical breakdowns.
Because the electrostatic force is short-range, the stroke of an electrostatically driven micropump is relatively small. The deflecting force is quadratically proportional to the distance between the electrodes. For example, the stroke of known micropumps can be as little as 5 μm, which results in a stroke volume of only about 40 nl. If the dead volume is large, the compression ratio will be very low. Known micropumps are not bubble resistant and are not suitable for compressible media such as air, making micropumps practically impractical.
Furthermore, known micropumps are assembled manually to prevent electrical contact and short circuits between the counter electrode and the diaphragm when using the required high supply voltages of 200V or more. Assembling chips manually is completely uneconomical.

On the other hand, electrostatically driven micropumps made of silicon may have many advantages compared to piezoelectrically driven micropumps.
・Full wafer level processing in a standard MEMS fab with no piezo bonding ・All process steps are established silicon microfabrication techniques at wafer level ・Piezo placement, adhesive dosing, bonding There are no manufacturing tolerances due to chemical gardening, etc. ・All mechanical parts are made of silicon and do not use ceramics, so there is no fatigue or micro-cracks during long-term operation ・Material is only silicon (no Pb like PZT piezoelectric material, RoHS compliant) satisfied)
・Can operate at extremely high temperatures, estimated at up to 800°C (in case of silicon only, depends on the material of the electrical interface)
・Hysteresis does not occur because there is no piezoelectric material. ・100 pF for capacitance of 2 nF (for piezoelectric material): low energy consumption.

・Possibility of miniaturization:
○ Piezoelectric drive is limited to ceramic pick-and-place, so it is not possible to achieve anything smaller than 3 x 3 mm2. ○ Electrostatically driven pumps can achieve even smaller dimensions (2 x 2 mm2, perhaps even 1 x 1 mm2). ○The stroke of electrostatic actuation (approximately 5 μm at 200V) is almost independent of the chip size. In the case of piezoelectric actuation, the stroke also depends on the chip size.
・2x2mm2 micro pump:
○8000 micropumps per 8 inch wafer ○Manufacturing cost is approximately 10 cents for over 200 wspw Although the advantages of electrostatically driven micropumps are numerous compared to piezoelectrically driven pumps, electrostatically driven micropumps are not commercially available. It has not been.
There is a need to provide electrostatic micropumps that are configured to be manufactured at the wafer level while minimizing the risk of short circuits. The present invention overcomes the drawbacks of known electrostatically driven micropumps and enables the advantages mentioned above.

Generally, the stroke volume of the electrostatically actuated diaphragm should be fairly high and the blocking pressure should be high enough to overcome the drawbacks of known electrostatically actuated micropumps. The process should then be able to match a valve unit with a sufficiently small dead volume in the pump chamber to the actuating unit to achieve a high compression ratio. Furthermore, the pump should be able to be assembled on a complete wafer level to electrically isolated or insulated electrodes. The electrodes then need to be accessed after dicing the wafer into pump chips and should not risk shorting at the edges.

One embodiment according to the invention is an electrostatic micropump comprising a diaphragm device including a diaphragm and a first electrode structure. The electrostatic micropump further includes a valve device including an inlet check valve and an outlet check valve, the diaphragm device and the valve device at least partially surrounding the pump chamber. The electrostatic micropump further comprises a second electrode structure arranged to form an electrostatic drive with the first electrode structure. The electrostatic actuator is configured to deflect the diaphragm. The micropump further comprises at least one anti-stiction bump disposed between the first electrode structure and the second electrode structure, and in the non-operating state of the micropump, the first electrode structure and The spacing between the second electrode structure varies from a peripheral region of the pump chamber towards a central region of the pump chamber, the peripheral region surrounding the central region.
In the operating state of the micropump, the diaphragm is configured to deflect due to the electrostatic drive formed by the first electrode structure and the second electrode structure.
At least one anti-stiction bump is disposed between the first and second electrode structures to prevent the diaphragm from sticking to the second electrode structure.

In a preferred embodiment, the first electrode structure and/or the second electrode structure have a variable height configuration, such that the spacing between the first electrode structure and the second electrode structure is adjusted in the pump chamber. Increase from the peripheral area towards the central area.
The variable height shape of at least one of the two electrode structures is configured to enlarge the pump chamber and/or the stroke volume of the pump chamber. Additionally, the variable height geometry reduces the minimum distance between the first and second electrode structures, thereby reducing the required voltage and/or energy usage of the electrostatic drive. can be done.
The variable height geometry of the counter electrode theoretically has a limited effect on the stroke volume since it forms a mechanical stop. Therefore, it is important to select a height profile that reduces operating voltage and increases rather than reduces stroke volume.
The volume between the electrodes in the actuated state, ie between the movable electrode and the rigid electrode, may be approximately half the volume between the electrodes in the non-actuated state.

According to one embodiment, at least one anti-stiction bump is arranged on the first or second electrode structure opposite the variable height shape.
The at least one anti-stiction bump may be located on the second electrode structure that is neither the first electrode structure nor the diaphragm device. At least one anti-stiction bump may be disposed on the second electrode structure opposite the variable height shape. Anti-stiction bumps may be present between the first and second electrode structures, e.g. when the supply voltage exceeds the pull-in voltage and/or when the diaphragm is pressed against the counter electrode by hydrostatic pressure, for example. Reduces the risk of sticking between the parts. The at least one anti-stiction bump reduces the occurrence of both electrostatic sticking when the pull-in voltage is exceeded and van der Waals sticking caused by hydrostatic pressure.
Placing the anti-stiction bump on a flat surface, for example, opposite the variable height feature allows easy placement or generation of the anti-stiction bump, and the precision of the variable height feature improves the anti-stiction It can be made unaffected by the generation of bumps.
One problem with using electrostatic actuation is electrostatic sticking. When a high voltage is applied, the two parts come into contact with each other. In such a situation, a very high electric field is generated within the insulating layer and the charge (driven by this high electric field) can be relaxed into the insulating layer across the boundary of the two parts. Thereafter, when the voltage is removed, the charge remains in the insulating layer and electrostatic sticking occurs. To overcome the situation, one promising strategy is to reduce the contact area to which high electric fields are applied, for example by anti-stiction bumps. The function of anti-stiction bumps is to reduce the contact area between hard materials, reducing the area over which charges can be relaxed. Electrostatic sticking is reduced by the ratio of the contact area with the bump to the contact area without the pump. Additionally, the beneficial ratio also reduces van der Waals sticking. Additionally, bipolar (eg, -200V to 200V) drive voltage of the actuator or micropump also reduces the effects of electrostatic sticking.

Regarding bump design, there are the following boundary conditions. The height of the bump should be as small as possible since it reduces the stroke of the actuator. Regarding etching techniques, heights of 10 nanometers to 200 nanometers are achievable. Small gaps are sufficient to avoid charge relaxation in these regions.
The contact area of all bumps should be much smaller compared to the contact area without the pump (to reduce sticking). However, if the total contact area of all bumps is too small, the entire force will be concentrated on this small area and may exceed the mechanical stability of the bumps. Electrostatic compressive forces on the bumps can cause damage to the bumps. For this purpose, this contact area should be selected to be significantly below the maximum mechanical stress that can be applied. For single crystal silicon, this value is approximately 4 GPa, and for silicon oxide it is a smaller value.

According to an embodiment, the spacing between the first electrode structure and the second electrode structure increases in steps from the peripheral region towards the central region of the pump chamber.
A stepwise increasing height profile from the peripheral region to the central region of the pump and/or electrode chamber can reduce the minimum distance between the first electrode structure and the second electrode structure. , the resulting lower supply voltage requirements reduce the energy usage of the micropump and allow the use of compact and well-established circuits for high voltage generation.
In a preferred embodiment, mechanical contact is provided to the first electrode structure and the second electrode structure in the peripheral region, and electrical penetration between the first electrode structure and the second electrode structure is provided. The first electrode structure and the second electrode structure are insulated from each other by an insulating layer that prevents the occurrence of.
Since the first electrode structure and the second electrode structure form an electrostatic drive for deflecting the diaphragm, there is electrical penetration between the first electrode structure and the second electrode structure. If this occurs, the electrostatic force to deflect the diaphragm may be small. That is, electrical penetration between the two electrode structures is undesirable and is prevented by an insulating layer between the two electrode structures.

In a preferred embodiment, the electrostatic drive is configured to vary the pressure within the pump chamber and/or the volume of the pump chamber based on the voltage between the first electrode structure and the second electrode structure. configured.
The electrostatic drive formed by the first and second electrode structures exerts pressure on the pump chamber, the force being dependent on the voltage between the first and second electrode structures. . Since the voltage between the first electrode structure and the second electrode structure can be changed in small steps, the micropump can intentionally set the volume and/or pressure of the pump chamber in small steps. It becomes a practical device.

In a preferred embodiment, the valve device is a layer device. The inlet check valve and the outlet check valve are arranged in-plane with respect to the valve arrangement. Both inlet and outlet check valves include an inlet tunnel, a valve flap, an outlet tunnel, and a dead volume such that fluid flow through the inlet tunnel, the open valve flap, and the outlet tunnel. configured to guide The direction of fluid flow through the inlet check valve is opposite the direction of fluid flow through the outlet check valve.
The electrostatic micropump includes at least one inlet check valve and at least one outlet check valve. In order to reach quick and/or cheap manufacturing, the inlet check valve and the outlet check valve may be arranged in a layer device, the inlet check valve and the outlet check valve being arranged in the same plane as this layer. be done. To further reduce the complexity of the valve arrangement, the same or similar check valves can be used for the inlet check valve and the outlet check valve, and the inlet tunnel of the inlet check valve is similar to that of the outlet check valve. It faces the opposite direction of the entrance tunnel.
In a preferred embodiment, the diaphragm device comprises a conductive layer that is at least part of the first electrode structure.
If the diaphragm of the diaphragm device is made of a non-conductive material, the diaphragm device comprises an additional conductive layer that is part of the first electrode structure.
In a preferred embodiment, the valve device comprises a stack of semiconductor layers and has a thickness of eg 480 μm to 540 μm perpendicular to the major surface of the valve device and/or the diaphragm device has a thickness of eg 10 μm perpendicular to the major surface of the diaphragm device. A semiconductor layer with a thickness of ˜120 μm is provided.

In a preferred embodiment, the valve device comprises a conductive layer that is at least part of the second electrode structure. One embodiment of the invention can be realized by attaching a diaphragm device to a valve device. Both the diaphragm device and the valve device include a conductive layer that is at least part of the first electrode structure or the second electrode structure, or are made of such a conductive material. The pump chamber is formed by a valve device and a diaphragm device.
In a preferred embodiment, the electrostatic drive is configured such that, when actuated, the diaphragm deflects the diaphragm toward the valve device to compress the pump chamber and cause fluid to flow from the pump chamber through the outlet check valve and into the environment. be done.
According to one embodiment, the fluid flowing from the pump chamber through the outlet check valve is a non-conductive fluid.
The non-conductive fluid prevents electrical penetration between the first and second electrode structures forming the pump chamber. Electrical penetrations are undesirable because they reduce the force compressing the pump chamber.
In a preferred embodiment, the valve device comprises a stack of semiconductor layers, such as silicon layers, with a thickness of for example 480 μm to 540 μm perpendicular to the major surface of the valve device, and/or the diaphragm device comprises a stack of semiconductor layers, such as silicon layers, and/or a diaphragm device comprises a stack of semiconductor layers, such as silicon layers, with a thickness of eg 480 μm to 540 μm perpendicular to the major surface of the valve device. A vertical semiconductor layer such as a silicon layer with a thickness of 10 μm to 120 μm is provided.

According to one embodiment, an electrostatic pump includes a stator structure. A diaphragm device is positioned between the valve structure and the stator structure such that the stator structure and diaphragm device surround the electrode chamber. The stator structure includes a conductive layer that is at least part of the second electrode structure.
The electrostatic micropump may include a stator structure, a diaphragm device, and a valve device. A stator structure is attached to the diaphragm device and forms an electrode chamber. A diaphragm device is further attached to the valve structure to define a pump chamber, and the diaphragm device is between the stator structure and the valve device. In this embodiment, the diaphragm device includes a first electrode structure and the stator structure includes a second electrode structure.
In one embodiment, the electrostatic drive, when actuated, deflects the diaphragm device toward the stator structure to expand the pump chamber such that fluid flows through the inlet check valve and into the pump chamber. configured.
The static drive is formed by first and second electrode structures, ie a stator structure and a diaphragm device. The stator structure remains mechanically stable during operation, and the diaphragm device deflects toward the stator structure, thereby compressing the electrode chamber and expanding the pump chamber. As the pump chamber expands, the pressure within the pump chamber decreases, allowing fluid to flow from the environment through the inlet check valve and into the pump chamber.

According to one embodiment, the fluid flowing into the pump chamber through the inlet check valve is an electrically conductive or non-conductive fluid.
If the micropump of the invention comprises a separate electrode chamber and a separate pump chamber, the first and second electrode structures form the electrode chamber. In this case, the fluid flowing within the pump chamber does not contact both electrode structures, so the conductivity of the fluid does not affect the pumping performance of the electrostatic micropump.
According to one embodiment, the stator structure comprises a semiconductor layer, such as a silicon layer, and has a thickness perpendicular to the main surface of the valve arrangement, for example 450 μm.
In a preferred embodiment, the stator structure has a high stiffness compared to the diaphragm device.
Electrostatic micropumps that have a rigid stator structure, or at least a stator structure that is more rigid than the diaphragm device, when actuated, the diaphragm device remains stable or mechanically stable while the stator structure remains stable or mechanically stable. has the advantage of being a moving part.

According to one embodiment, the electrostatic micropump includes a vent configured to fluidly connect the electrode chamber with the environment of the electrostatic micropump.
The vent connecting the electrode chamber with the environment acts as a pressure equalizer between the electrode chamber and the environment. In this case, atmospheric pressure does not change the zero or inactive position of the diaphragm. That is, a high compression ratio can be achieved with a flat diaphragm and no back pressure is created within the electrode chamber when the diaphragm moves.
In preferred embodiments, the vent is configured to prevent contamination of the electrode chamber by using serpentines, high flow resistance, or capillary stops.
Contamination of the electrode chamber can reduce the mobility of the diaphragm, can reduce the volume of the electrode chamber, and/or can reduce the volume of the electrode chamber between the first and second electrode structures. Electrical penetration can occur, increasing the voltage and/or electrostatic force required between the two electrode structures to deflect the diaphragm. Various methods such as meandering, high flow resistance, and/or capillary stops prevent contamination of the electrode chamber.
According to one embodiment, the vent comprises a filter and/or buffer volume configured to prevent contamination of the electrode chamber.
Contamination of the electrode chamber can be further prevented by using a contaminated buffer volume in place of the electrode chamber and/or a filter to remove contamination.

According to one embodiment, the diaphragm of the diaphragm device is pre-deflected.
Instead of using vents, the diaphragm device may be pre-deflected. The pre-deflected diaphragm device further reduces the distance between the first and second electrode structures and reduces the force and/or pressure required to compress the electrode chamber and expand the pump chamber. Or the voltage can be reduced. The diaphragm device may be bonded to the stator structure in a vacuum. The degree of pre-deflection may depend on the vacuum applied.
In a preferred embodiment, the diaphragm device is pre-deflected to form mechanical contact with the stator structure in the non-actuated state of the electrostatic drive in the contact area, and the electrostatic drive in the actuated state forms a mechanical contact with the stator structure. adapted to increase.
The electrostatic force depends secondarily on the distance between the first and second electrode structures. A pre-deflected diaphragm device reduces the distance between the electrode structures and may require much less supply voltage to deflect the diaphragm device. A further advantage of the pre-deflected diaphragm device in contact with the stator structure is that the height of the electrode chamber can be increased, i.e. the volume of the pump chamber is increased when the micropump is activated. .

In a preferred embodiment, the conductive layer of the first electrode structure and the conductive layer of the second electrode structure are made of a conductive material such as a metal material, or a material having the conductivity of a metal material such as boron or phosphor and silicon. Made of highly doped semiconductor material.
Further embodiments according to the invention produce respective methods.
However, it should be noted that the method is based on the same considerations as the corresponding device. Furthermore, the methods may be supplemented by any of the features or functionality described herein individually and in combination with respect to the apparatus.
In the following, embodiments of the disclosure will be explained in more detail with reference to the drawings.

1 is a schematic side view of an electrostatic micropump with three layers, according to one embodiment; FIG. 1 is a schematic side view of an electrostatic micropump with four layers, according to one embodiment; FIG. 2 is a schematic side view of a first layer and a second layer provided by a step of manufacturing an electrostatic micropump, according to one embodiment; FIG. FIG. 4 is a schematic side view of the second layer and a top view of the etching mask that can be obtained when the second layer is etched first, according to an embodiment for manufacturing a micropump; FIG. 3 is a schematic side view of the second layer that can be obtained when etching the second layer a second time with or without vents, and a top view of the etching mask, according to an embodiment for manufacturing a micropump; . 2 is a schematic side view of an insulated first layer and an insulated second layer that can be obtained when oxidizing the first and second layers according to an embodiment for manufacturing a micropump; FIG. . Schematic side view of an insulated second layer with anti-stiction bumps that can be obtained when etching anti-stiction bumps in the insulated second layer according to an embodiment for manufacturing a micropump and a top view of an etching mask with a dot pattern. Schematic side view of an insulated first layer and an etching mask with a frame shape obtainable when etching away the frame region of the insulated first layer, according to an embodiment for manufacturing a micropump; FIG. 2 is a schematic side view of an actuator device at chip level that can be obtained when attaching an insulated first layer to an insulated second layer according to one embodiment for manufacturing a micropump; FIG. Schematic side view of a multiple actuator device at wafer level that can be obtained when attaching an insulated first layer wafer to an insulated second layer wafer, according to one embodiment for manufacturing a micropump. It is a diagram. 2 is a schematic side view of an actuator device obtainable when removing an insulating layer from the main surface of the actuator device according to an embodiment for manufacturing a micropump; FIG. 2 is a schematic side view of an actuator device obtainable when thinning the first layer of the actuator device according to one embodiment for manufacturing a micropump; FIG. 2 is a schematic side view of an actuator device that can be obtained when depositing a conductive material on the main surface with a first layer of the actuator device, according to an embodiment for manufacturing a micropump; FIG. 2 is a schematic side view of an actuator device obtainable upon removal of conductive material from the surrounding area, according to one embodiment for manufacturing a micropump; FIG. 1 is a schematic side view of a wafer testing apparatus configured to test an actuator device, according to one embodiment; FIG. FIG. 2 is a schematic side view of an actuator device according to one embodiment. FIG. 4 is a schematic side view of a full-loop variation of an actuator device according to one embodiment; FIG. 2 is a schematic side view of a micropump according to one embodiment. FIG. 5 shows a table of simulated values for an electrostatic micropump design according to an embodiment. FIG. 2 is a schematic side view of a micropump with a vent, according to one embodiment. FIG. 3 is a schematic top view of a vent with a buffer volume and a capillary stop, according to one embodiment. FIG. 3 is a schematic top view of a reduced cross-section vent according to one embodiment; FIG. 3 is a schematic top view of a vent with serpentine sections, according to one embodiment. FIG. 2 is a schematic top view of a vent with a filter, according to one embodiment. FIG. 3 is a schematic top view of a vent with a buffer volume, according to one embodiment. 1 is a schematic side view of a micropump with a pre-deflected diaphragm in an unactuated state, according to one embodiment; FIG. 1 is a schematic side view of a micropump with a pre-deflected diaphragm in an actuated state, according to one embodiment; FIG. A known micropump is shown.

Various embodiments and aspects of the invention are described below. Further embodiments are also defined by the appended claims.
It is noted that any embodiment defined by the claims may be supplemented by any of the details, features, and functionality described herein. Also, the embodiments described herein may be used individually and optionally supplemented with any of the details, features and functionality falling within the scope of the claims.
It is also noted that the individual aspects described herein can be used individually or in combination. Thus, details may be added to each of the aspects without adding detail to another of the individual aspects. Note also that this disclosure explicitly or implicitly describes features that can be used with electrostatic micropumps. Therefore, any of the features described herein can be used in the context of electrostatic micropumps. Furthermore, the features and functions disclosed herein in connection with methods may also be used in devices configured to perform such functions.
Furthermore, any features and functionality disclosed herein with respect to the device may be used in a corresponding manner. In other words, the methods disclosed herein may be supplemented with any of the features and functionality described with respect to the apparatus.
The present invention will be more fully understood from the following detailed description and accompanying drawings of embodiments of the invention, which should not be construed to limit the invention to the specific embodiments described. It should not be used, but is only for explanation and understanding.

FIG. 1 shows a schematic side view of an electrostatic micropump 100 comprising three layers 101, 102, 103, according to one embodiment. Although layers 101, 102, 103 are described as one layer, one or more of them may be formed by multiple stacks of the same or different materials. Layer 101, layer 102 and layer 103 may include a semiconductor material, such as a silicon material. Layer 101, layer 102 and layer 103 may comprise any suitable thickness, with preferred values being layer thicknesses within a tolerance range of approximately ±50%, ±30 or ±20%, e.g. 450 μm, layer 102 may be 30-90 μm and layer 103 may be 10-120 μm.
The major surface of layer 101 is attached to the major surface of layer 102 to form a valve arrangement 120 comprising an inlet check valve 160 and an outlet check valve 170. Inlet check valve 160 and outlet check valve 170 are arranged in-plane with respect to valve arrangement 120 . Inlet check valve 160 and outlet check valve 170 may have similar construction, allowing fluid to flow in opposite directions in the open state.

Layers 101 and 102 may have a particular structure that forms valves 160 and 170 when attached to each other. For example, the structure formed by layers 101 and 102 may include one or more of apertures and fluid conducting channels such as inlet tunnel 130 and/or outlet tunnel 150. For example, some of the components, such as valve flap 140, may be deflectable in response to fluid flow and/or fluid pressure. For example, some portions, such as dead volume 106, may be formed by empty space that allows for deflection of the deflectable component.
A major surface of valve device 120 is attached to a first major surface 185 of diaphragm device 180 .

The diaphragm device 180 comprises a layer 103 that can be insulated from the valve device 120 by an insulating layer 104 on a first major surface 185 of the diaphragm device 180, for example a silicon dioxide layer or a silicon nitride layer. The recess 195 may be, for example, the remains of an insulating gap used to facilitate dicing, as described in connection with FIG. 14.
Both valve device 120 and diaphragm device 180 may include electrode structures. The diaphragm device 180 includes a first electrode structure 109 and the valve device 120 includes a second electrode structure 108, the first electrode structure being insulated from the second electrode structure by an insulating layer 104. . First electrode structure 109 and second electrode structure 108 form an electrostatic drive configured to deflect diaphragm device 180 . The electrode structure may be a separate layer, as shown in FIG. 1, but may include at least one layer of conductive material, such as, for example, a metallic material or a doped semiconductor material or a combination thereof. This may be done by providing the material.

In the central region 190 of the micropump 100 comprising the inlet valve 160 and the outlet valve 170, the first major surface 185 of the layer 103 or diaphragm device 180 has a stepped variable height profile 107 and one or more stiction prevention bumps 105. The distance between the diaphragm device 180 and the layer of the valve device 120, obtained at least in part by the variable height feature 107 on the first major surface 185 of the diaphragm device 180, creates a volume that may be referred to as a pump chamber 110. It is possible. Alternatively or additionally, the anti-stiction bump 105 may also be arranged on the opposite side of the pump chamber 110, ie on the valve device 120.

Electrostatic micropump 100 is configured to operate by applying a voltage between first electrode structure 109 and second electrode structure 108 . The voltage between the electrode structures creates a force that compresses the pump chamber 110. The force depends secondarily on the distance between the first electrode structure 109 and the second electrode structure 108.
The stepped variable height configuration 107 is particularly advantageous when compared to the voltage and/or energy usage required to compress the pump chamber at a constant distance height configuration when implementing a membrane structure without pre-deflection. The voltage and/or energy usage required to compress pump chamber 110 may be reduced. If the voltage between the electrode structures 108, 109 is high and higher than the retraction voltage, the first electrode structure 109 will be attracted to the second electrode structure 108 such that the diaphragm device 180 can contact the valve device 120. It will be done. To prevent sticking of the diaphragm device 180 to the valve device 120, at least one anti-stiction bump 105 is disposed between the first electrode structure 109 and the second electrode structure 108. Ru. For example, anti-stiction bump 105 of FIG. 1 is disposed on diaphragm device 180 in region 190 that includes the inlet and outlet check valves. However, one or more anti-stiction bumps 105 may alternatively or additionally be arranged opposite the variable height shape, for example in each of the layer 102 and the valve device 120.

By activating the electrostatic drive of the micropump 100, the diaphragm device 180 is drawn toward the valve device 120 while compressing the pump chamber 110. Compression of the pump chamber 110 increases the pressure within the pump chamber 110 and opens the valve flap 140 of the outlet check valve 170, allowing fluid to exit the pump chamber 110 through the outlet check valve 170 to the environment. .
Reducing the voltage between the first electrode structure 109 and the second electrode structure 108 causes the diaphragm device 180 to move toward its initial or zero position, while expanding the pump chamber 110. You can move back inside. Expansion of pump chamber 110 causes valve flap 140 of inlet check valve 160 to open, allowing fluid to flow from the environment through inlet check valve 160 and into pump chamber 110 . At the same time, by blocking fluid flow through the outlet tunnel 130 with the valve flap 140, the check valve 170 may block fluid flow through the outlet tunnel.

The electrostatic micropump 100 of FIG. 1 has several advantages compared to prior art micropumps. The stepped variable height configuration 107 of the pump chamber 110 may operate with a low supply voltage compared to that of prior art micropumps. This low supply voltage, although still within the high voltage range, is considered low compared to the supply voltage of prior art micropumps. This lower supply voltage reduces the energy usage of electrostatic micropump 100 and allows the use of compact, well-established high voltage circuits.
As a further advantage, operating electrostatic micropump 100 may overcome some backpressure. The back pressure prevents movement of the diaphragm device 180. Increasing the supply voltage increases the static voltage that overcomes the back pressure.
Electrostatic micropumps 100 for non-conductive fluids such as air have a high compression ratio, which can be higher than electrostatic micropumps for conductive fluids such as micropump 200 of FIG. This is because the deflection of diaphragm device 120 is directed toward pump chamber 110 and may reduce additional dead volume 106.

FIG. 2 shows a schematic side view of an electrostatic micropump 200 with four layers 201-204, according to one embodiment. Although layers 201-204 are described as one layer, one or more of them may be formed by multiple laminates of the same or different materials. Layers 201-204 may include semiconductor materials, such as silicon materials, for example. The layers 201 to 204 have a thickness of, for example, 450 μm, 30-90 μm, 10-120 μm and 450 μm, respectively, and may optionally be within a tolerance range of, for example, ±50%, ±30 or ±20%.
Region 295 may be the remains of a trench structure used or created to facilitate dicing, for example as described in connection with FIG. 1.
The major surface of layer 201 is attached to the major surface of layer 202 to form a valve device 220 similar to valve device 120 of FIG. The valve device 220 includes an inlet check valve 260 and an outlet check valve 270 arranged in the layer device, and the inlet tunnels of the inlet check valve 260 and the outlet check valve 270 are similar to the inlet check valve 160 and the outlet check valve 270 of FIG. Like the outlet check valve 170, it faces in the opposite direction.

A major surface of valve device 220 is attached to a first surface 285 of diaphragm device 230 that includes layer 203 and first electrode structure 210 . The valve device 220 and the diaphragm device 230 are mounted to form a pump chamber 207 in at least a central region 290 of the micropump 200 comprising an inlet check valve 260 and an outlet check valve 270.
Diaphragm device 230 is disposed between valve device 220 and stator structure 240. The stator structure comprises a layer 204 and a second electrode structure 211 . First main surface 245 of layer 204 is insulated by insulating layer 205 . Insulated layer 204 is attached to second major surface 288 of diaphragm device 230 .
The first surface 245 of the layer 204 has a stepped variable height configuration in a central region 290 of the micropump 200 that includes, at least in part, an inlet check valve 260, an outlet check valve 270, and a stepped variable height configuration 209. 209 and at least one anti-stiction bump 208. The second major surface 288 of the diaphragm device 230 and the first major surface 245 of the stator structure 240 form an electrode chamber 212 in a region 290 that includes the stepped variable height feature 209 .

The first electrode structure 210 and the second electrode structure 211 form an electrostatic drive for deflecting the diaphragm device 230. The electrode structure may be a separate layer, as shown in FIG. 2, but may include at least one layer of conductive material, such as, for example, a metallic material or a doped semiconductor material or a combination thereof. This may be done by providing the material.
In operation, diaphragm device 230 deflects toward stator structure 240 when a voltage is applied between first electrode structure 210 and second electrode structure 211 . Since the stator structure 240 is more rigid than the diaphragm device 230, it can be considered that the diaphragm device 230 flexes towards the stator structure 240 while the stator structure does not. When micropump 200 is activated, diaphragm device 230 compresses electrode chamber 212 and expands pump chamber 207. Expansion of pump chamber 207 opens inlet check valve 260, allowing fluid to flow from the environment through inlet check valve 260.

Reducing the voltage between the first electrode structure 210 and the second electrode structure 211 causes the diaphragm device 230 to deflect toward or back to its initial or zero position, causing the electrode chamber 212 may expand and pump chamber 207 may be compressed. Compression of pump chamber 207 increases the pressure within pump chamber 207 and opens outlet check valve 270, allowing fluid to exit pump chamber 207 through outlet check valve 270 and into the environment. At the same time, by blocking the inlet tunnel with a valve flap, the inlet check valve 260 may block fluid flow through the inlet tunnel.
A stepped variable height shape 209, similar to the height shape 107 of FIG. The voltage and/or energy usage required to deflect the diaphragm device 230 is reduced compared to a micropump with a pump chamber having a diaphragm device 230.
Sticking of diaphragm device 230 to stator structure 240 is prevented by at least one anti-stiction bump 208 similar to anti-stiction bump 105 of FIG. An anti-stiction bump or additional anti-stiction bump 208 may be disposed on the second surface 288 of the diaphragm device 230 opposite the variable height shape of the layer 204.

Unlike the micropump 100 of FIG. 1, which is configured to pump non-conductive fluids, the electrostatic micropump 200 pumps both conductive and non-conductive fluids because the fluid does not contact the electrode structure. Configured to pump. Pump chamber 110 in FIG. 1 is formed by first electrode structure 109 and second electrode structure 108. Pump chamber 110 in FIG. The conductive fluid within pump chamber 110 may cause electrical penetration between first electrode structure 109 and second electrode structure 108 of FIG. In contrast, in FIG. 2, electrostatic micropump 200 is configured to pump both conductive and non-conductive fluids. The first electrode structure 210 and the second electrode structure 211 form an electrode chamber 212 and fluid flows within the pump chamber 207 . Because there is no fluid connection between pump chamber 207 and electrode chamber 212, electrostatic micropump 200 can also pump electrically conductive fluid.

As described in further embodiments, the required supply voltage and/or energy usage may be further reduced by a vent that fluidly connects the electrode chamber 212 with the environment to allow pressure compensation within the electrode chamber 212.
Electrostatic micropumps can be reasonable if they are bubble-resistant, can be manufactured entirely at wafer level, and can be electrically connected without risk of short circuits. Electrostatic micropumps with diaphragms are equally suitable for practical use as piezoelectrically driven micropumps, but have some additional advantages compared to piezoelectric micropumps.
For example, electrostatic micropumps with electrostatic diaphragms have low energy consumption. The capacity to be charged of an electrostatically driven micropump with a diaphragm may be about an order of magnitude smaller than that of a piezoelectrically driven micropump.

Compared to micropumps assembled with comparable layer materials and driven by piezoceramic drives, embodiments have only one temperature expansion when the electrostatic drive is a semiconductor drive, such as a silicon drive. In the case of piezoceramic drives, there is no additional temperature expansion, which allows a pump with higher temperature stability.
The subject matter of the present disclosure is that the electric field force of an electrostatic drive does not vary with temperature and therefore is more temperature sensitive compared to a piezoceramic drive. In contrast, the polarization of piezoelectric ceramics disappears once the Curie temperature is reached.
The subject matter of the present disclosure is that the electrostatic drive has a higher mechanical resistance, since it comprises, for example, ideally elastic monocrystalline silicon, as opposed to defective polycrystalline piezoceramics and adhesives.
Compared to micropumps driven by piezoceramic drives, the subject of the present application is that electrostatic drives are easy to manufacture, since they can be manufactured by MEMS standard processes in front-end manufacturing plants.
The subject matter of the present application is that miniaturization is possible because the physical principles of the electrostatic drive and the electrode surface can be scaled independently and advantageously over short distances.
The subject matter of the present application is low supply chain costs and economy, as the manufacturing of electrostatic drives has few process steps and/or few supply chain participants.
After introducing the micropump embodiment of FIGS. 1 and 2, manufacturing steps of the micropump embodiment will be described with reference to the following figures.

FIG. 3 shows a schematic side view of a first layer and a second layer obtained by a first step of an embodiment for manufacturing an electrostatic micropump, such as micropump 200 of FIG. 2. FIG. The first step is to provide a first layer 301 and a second layer 302. Terms such as first step, second step, etc. do not necessarily refer to a first step, but are used to distinguish between steps. Similarly, such representation does not necessarily limit the order of steps.
The first layer 301 may be a diaphragm device similar to diaphragm device 230 of FIG. 2, and the second layer 302 may be a stator structure similar to stator structure 240 of FIG.
For example, both layers may be part of a wafer, ideally made of polished single crystal silicon, where X represents the polished surface of the given layer. Similar to silicon wafers, both wafers may be P+ or N+ doped as shown in Table 303. Thus, both layers may be N+ or P+ doped, or the first layer may be N+ doped and the second layer P+ doped.
Both wafers may be, for example, single side polished (SSP) 8 inch heavily doped wafers with a thickness of eg 750 μm and a resistivity of eg 0.001 to 0.1 ohm centimeters. Markings such as conditioning markings or bonding markings for further processes such as etching processes may be applied to the polished surface of the wafer.

FIG. 4 is a schematic side view of a second layer 302 that may be obtained by first etching the second layer 302, according to one embodiment for manufacturing an electrostatic micropump, such as the micropump 200 of FIG. shows. FIG. 4 further shows a top view of an etch mask configured to be used to etch the second layer 302 at the polished major surface.
The second layer may have a circular shape, for example to create a circular pump chamber or a step therein, in the area 405 of the wafer intended to be the central area of the micropumps that are later diced. A mask 420 is used to etch to a depth of approximately 3 μm, for example. Etch depth and/or mask shape may vary depending on wafer attributes, pumping requirements, etc. Etched region 405 becomes the first step of a stepped variable height shape similar to stepped variable height shape 209 of FIG.

FIG. 5 shows a schematic side view of a second layer 302 that may be obtained by etching the second layer 302 a second time, according to one embodiment for manufacturing an electrostatic micropump, such as the micropump 200 of FIG. Show the diagram. FIG. 5 further shows top views of various etch masks 510, 520, 530, 540 configured to be used to etch the second layer 302 a second time.
The second layer 302 of FIG. 4 has a shape, e.g. a circular shape, similar to the shape of the mask 420 of FIG. A mask 510 is etched again on the polished main surface to a depth of approximately 3 μm. Etched region 505 and/or mask 510 has a different diameter than central region 405 and/or mask 420 of FIG. Etched region 505, together with etched region 405, forms a stepped variable height shape 560 similar to stepped variable height shape 209 of FIG.

Alternatively, second layer 302 may be etched on the polished main surface by mask 520, mask 530, or mask 540. Masks 520, 530, and 540 are similar in that they are configured to etch or form a circular chamber with a vent 550. Vent 550 is configured to connect the electrode chamber with the environment of the electrostatic micropump.
Etch masks 520 and 530 show examples of different angles of the vents. Etching mask 540 is configured to etch more than one, eg, four, electrode chambers with respective vents 550 to form more than one, eg, four, micropumps. The etch process may use SPTS non-switching process management. The depth of the etched chamber may vary from wafer to wafer.

FIG. 6 shows an insulated micropump that can be obtained by oxidizing a first layer 301 and a second layer 302, according to one embodiment for manufacturing an electrostatic micropump, such as the electrostatic micropump 200 of FIG. A schematic side view of a first layer 301 and an insulated second layer 302 is shown.
Both the first layer 301 and the etched second layer 302 are oxidized to form an oxide layer on their both major surfaces. The target thickness of the oxide layer is, for example, 400 nm, so that it acts as an insulating layer between the two electrode structures and prevents electrical penetration between them, for example at voltage values below 200V. The oxidation process forms an insulating oxide layer 610 similar to insulating oxide layer 205 of FIG. 2 on both sides of the major surfaces of layers 302 and 301.

FIG. 7 shows an insulating oxide layer 610 over the variable height feature 560 of the etched second layer 302, according to one embodiment for manufacturing an electrostatic micropump, such as the electrostatic micropump 200 of FIG. FIG. 3 shows a schematic side view of an insulated second layer 302 with anti-stiction bumps 708 that can be obtained by etching anti-stiction bumps 708. FIG.
FIG. 7 further shows a top view of an etch mask 710 configured to be used to etch anti-stiction bumps 708. The etch mask 710 used to etch the anti-stiction bump 708 comprises a circular shape 720 with a dot pattern 730.
The anti-stiction bumps 708 are etched by a dry or wet etching process using KOH to a very small target depth (e.g. between 20 nm and 200 nm; the target diameter of the anti-stiction pump 708 is e.g. 20 μm). It's okay. Anti-stiction bump 708 is similar to anti-stiction bump 208 of FIG.

FIG. 8 illustrates an insulated first layer 301 that can be obtained when the frame region 830 of the insulated first layer 301 is etched away, according to one embodiment for manufacturing a micropump, such as the micropump 200 of FIG. 3 shows a schematic side view of a layer 301 of FIG. For example, by using an etch mask 810 having a frame shape 820, a frame region 830, for example 36 μm deep, on the polished surface of the first layer 301 is etched away.
The first layer is prepared for a dicing process by etching away or thinning the frame region 830 of the first layer 301. For example, etching may be performed to a depth of about 36 μm using a dry etching process such as a dicing-by-thinning process.
Additionally, frame region 830 provides an insulating gap between adjacent diaphragm devices, allowing micropumps to be tested at wafer level during the manufacturing process.

9a and 9b illustrate the results obtained when attaching an insulated first layer 301 to an insulated second layer 302 according to one embodiment for manufacturing a micropump, such as micropump 200 of FIG. 2 shows a schematic side view of an actuator device that can be used. 9a shows a schematic side view of an actuator device at chip level 910, and FIG. 9b shows a schematic side view of a plurality of actuator devices at wafer level 940.
The major surface of the second layer 302 having the stepped height feature 560 and the anti-stiction bumps 708 is attached to the etched major surface of the first layer 301 . The first and second layers 301, 302 are attached by, for example, wafer bonding at 1050° C. for, for example, 4 hours. The first and second layers 301, 302 form an electrode chamber 930 similar to electrode chamber 212 of FIG.
First layer 301 and second layer 302 are joined together to form actuator device 920. The two layers 301, 302 are bonded together at wafer level 940, and the individual chips 910 have not yet been diced.
Actuator device 920 may include an insulating oxide layer 610 on both of its major surfaces.

FIG. 10 shows a schematic side view of an actuator device that can be obtained by removing the insulating layer 610 from the main surface of the actuator device 930, according to an embodiment for manufacturing a micropump, such as the micropump 200 of FIG. .
Removal of the oxide layer may be performed by a wet chemical process such as HF-Dip. By removing the insulating layer on the main surface of the actuator device 920, electrical contact can be made with the first layer and/or the second layer 301, 302.

FIG. 11 shows a schematic side view of an actuator device 930 that can be obtained when the first layer 301 of the actuator device 920 is thinned, according to an embodiment for manufacturing a micropump, such as the micropump 200 of FIG. . The thickness of the first layer 301 is determined in order to form a diaphragm from the first layer 301, i.e. to make the layer 301 deflectable and mechanically stable enough to avoid breakage when deflected. decrease the For example, the first layer 301 may be as thin as, for example, 750 μm to, for example, 30 μm.
For example, the thinning process may be performed by grinding the first layer 301 from 750 μm to 100 μm and then applying chemical mechanical polishing (CMP) to reach a thickness of, for example, 50 μm. The remaining 20 μm, for example, can be etched away by dry etching. First layer 301 is a diaphragm having a thickness in the same range as diaphragm device 230 of FIG.
If the diaphragm formed from the first layer 301 is a non-conductive diaphragm, deposition of an electrode structure on the diaphragm is recommended.

12 is obtained by depositing a conductive material 1210 on the main surface with the first layer 301 of the actuator device 920, according to an embodiment for manufacturing a micropump, such as the micropump 200 of FIG. 9 shows a schematic side view of an actuator device 920 obtained.
Deposition may be performed, for example, by sputtering a conductive material 1210, such as aluminum, onto the surface with the diaphragm formed from the first layer 301 of the actuator device 920. Conductive material 1210 may act as second electrode structure 210 of diaphragm device 230 of FIG.
The sputtering process may deposit the conductive material 1210 over the entire surface of the actuator device 920, rather than just directly over the diaphragm formed from the first layer 301, thereby increasing the conductivity between the diaphragms, as shown in FIG. Preferably, material 1210 is removed.

FIG. 13 is a schematic of an actuator device that can be obtained by removing conductive material from the peripheral region of a micropump without a diaphragm, according to one embodiment for manufacturing a micropump, such as the micropump 200 of FIG. A side view is shown.
Removing the conductive material 1210 from the peripheral area of the micropump that is subsequently diced, ie between the diaphragms formed from the first layer 301, is to insulate the diaphragms from adjacent diaphragms. Removal of conductive material may be accomplished by spray coating and wet chemical etching.
First layer 301 and conductive layer 1210 form a diaphragm device 1310 similar to diaphragm device 230 of FIG. 2 formed by layer 203 and second electrode structure 210.
Diaphragm device 1310 may be isolated from adjacent diaphragm devices 1310, allowing for wafer level testing in wafer test apparatus 1400, as shown in FIG. For example, trenches may be formed that can become traces 195 and/or 295.

FIG. 14 shows a schematic side view of a wafer testing apparatus 1400 configured to test actuator apparatus 920 at the wafer level. Test apparatus 1400 includes a chuck 1450 configured to hold actuator device 920 during testing. Test apparatus 1400 further includes a probe 1420 or wafer probe configured to test actuator apparatus 920.
Testing includes attaching the second layer 302 of the actuator device 920 to the chuck 1450, the actuator device 920 comprising the wafer of the second layer 302 and the plurality of diaphragm devices 1310.
Testing further includes placing probes 1420 one by one on diaphragm devices 1310 and testing or probing actuator devices 920 by applying a test voltage to actuator devices 920 or diaphragm devices 1310.
The diaphragm device 1310 does not include the diaphragm device 1310 and is insulated from the adjacent diaphragm device 1310 by an insulating gap 1480 in the peripheral area of the micropump that is later diced.

The sidewall insulation or insulation gap 1480 can be considered an essential feature of the micropump of the present invention. Sidewall insulation is an insulation between two electrode surfaces and/or a frame around at least one electrode surface, which can be formed by subsequent layer transformations such as etching and oxidation of the separation and/or by PECVD, PVD, etc. is produced by depositing an insulating layer using physical and/or chemical processes.
Isolation and isolation of the actuator or diaphragm device 1310 has the advantage of speeding up the manufacturing process and allows testing with wafer level based measurements.
Electrostatic micropumps differ from known micropumps that do not provide isolation from adjacent diaphragm devices 1310. In this embodiment, such as micropump 100, isolation from adjacent diaphragm devices 1310 is implemented. Isolation from adjacent diaphragm devices 1310 can also be implemented in a slightly modified form in the manufacture of micropumps for conductive liquids, such as micropump 200 in FIG.
The above-described manufacturing of the actuator device 920 produces a so-called short-loop variant of the actuator device 920. Alternatively, there are full loop variations of actuator device 920. A portion of the fabrication of the full loop variant is shown in Figures 15a-15c.

FIG. 15a shows a schematic side view of an actuator device 920 formed by attaching a major surface of the second layer 302 with a stepped height shape 560 and an anti-stiction bump 708 to the first layer 301. The second layer 302 may already be diced, as shown in FIG. 15a, or prepared for dicing by thinned frame regions, as shown in FIG. 15b.

FIG. 15b shows a schematic side view of a full loop variant of the actuator device 920, in which the first layer 301 is thinned in all areas and further thinned in areas 1510 of the stepped height shape 560. First layer 301 may include a conductive material. Etching 1510 defines the pump chamber height when no voltage is applied and the diaphragm is pressure balanced. In order to achieve a good compression ratio of the micropump and to make the pump bubble-resistant, this pump chamber height should be chosen very small. This height (1510 depth) can be considered an important design parameter for electrostatic micropumps. If high bubble resistance or high gas backpressure is required, this pump chamber height can be chosen very small (depending on the etching technique, such as dry etching or KOH etching). For example, from 50 nanometers to 1 μm.
A disadvantage when the height of the pump chamber is low is that the fluid resistance within the pump chamber is high. Therefore, if a high flow rate of the fluid (liquid or gas) is required, the pump chamber height 1510 can be selected from 1 μm up to 20 μm depending on the actuator stroke. The higher the pump chamber, the lower the fluid resistance and the higher the pump speed, but the compression ratio and bubble resistance will be lower.

FIG. 15c shows a schematic side view of a micropump 1570. Manufacturing a micropump 1570 similar to the micropump 200 of FIG. 2 is obtained by attaching the valve device 1550 to the actuator device 920. Pump chamber 1580 of micropump 1570 is formed by double etched region 1510 and valve device 1550.
Several differences between the short-loop and full-loop variants can be recognized. In the short loop variant, the diaphragms produced from layer 301 are diced and/or insulated from adjacent diaphragms, while in the full loop variant, the stator structures are diced and/or insulated from adjacent stator structures. or insulated.
Furthermore, in the full-loop variant, the pump chamber 1580 is etched into the first layer 301, whereas in the short-loop variant this need not be the case, and the pump chamber is formed by a diaphragm device and a valve device.
Furthermore, while in the full-loop variant the actuator device 920 is attached to, eg, joined to, the valve device, this need not be the case in the short-loop variant.

FIG. 16 shows a table of simulated possible implementations of electrostatically driven micropump designs. The exemplary simulated embodiments are not intended to limit the invention; electrostatically actuated micropumps can be manufactured in a vast range of chip sizes. Figure 16 shows simulation results for different chip sizes from 10 x 10 ^mm2 to 1 x 1 ^mm2 . The pump and actuation chambers are circular and the minimum distance to the square chip edge is 100 μm. Although the results are described in relation to quadratic chip sizes, the chips may have different aspect ratios on their sides, e.g. different from 1:1, e.g. rectangular in shape. Alternatively, an oval or circular shape or any other shape different thereto may be implemented.
Possible values for important attributes of an electrostatically actuated micropump design are listed below.

Data from an established piezoelectric micropump (KOH etched) was used to calculate the dead volume of the valve unit. For chip sizes less than 3 × 3 mm ² , dry-etched valves with small dead volume were assumed.
In this simulation, the design diameter and thickness were adapted to have a blocking pressure of approximately 30-53 kPa. The switching voltages and blocking pressures were compared to a reference design already implemented in the Fraunhofer EMFT. The working gap chamber height was chosen to be 5 μm for all designs and can be varied to higher or lower values by increasing or decreasing the switching voltage and stroke volume.
One relevant result of the simulation is the minimum and maximum air pressure that the pump can achieve depending on the compression ratio and the stiffness of the working diaphragm. This theory has been adapted in this simulation of an electrostatically driven pump. Considering the capillary pressure of the valve, it can be estimated that a bubble-resistant micropump should have an air backpressure close to or above 10 kPa. This concludes that, according to the table above, it is possible to realize electrostatically actuated micropumps with chip sizes up to 1.5 x 1.5 ^mm2 , which are not only capable of pumping liquids and gases but also bubble-resistant. be able to. With an optimized working chamber (not yet implemented in simulations), this goal can be achieved even in a 1 × 1 mm ² design.

Electrostatic micropumps with chip sizes of 2×2 mm ² or less are a major step towards low-cost, sustainable, and disposable devices that can be used, for example, in disposable lab-on-a-chip systems or smart electronic drug pills.
- Low cost: nearly 8,000 2x2mm ² pumps can be achieved for 8-inch wafers, making production costs less than 10 cents at very high volumes, e.g. starting over 100 wafers per week. It will be advantageous. Additionally, because no piezoelectric elements are used, the pump does not require pick-and-place or gluing.
- Sustainable disposable device: The silicon micropump, consisting only of a stack of silicon layers, does not contain any toxic substances such as lead in piezoelectric PZT. Silicon and silicon oxide consist of the same material as sand and a very thin layer of metal, such as gold or aluminum, on top. This makes it a completely sustainable component, with no problem disposing of the device as waste.

FIG. 17 shows a schematic side view of a micropump 1700 similar to micropump 200 of FIG. 2 with a vent 1720. The micropump includes a valve device 1760, a diaphragm device 1710, and a stator structure 1740. A major surface of valve device 1760 is attached to a major surface of diaphragm device 1710 to form pump chamber 1730. The major surface of the diaphragm device facing the pump chamber is attached to stator structure 1740. The stator structure includes a stepped variable height feature 1780 and a vent 1720. Diaphragm device 1710 is between valve device 1760 and stator structure 1740. The diaphragm device forms an electrode chamber 1750 with the stator structure 1740. A vent 1720 in stator structure 1740 connects electrode chamber 1750 with the environment.

An advantage of the vent 1720 is that the pressure within the electrode chamber 1750 is always ambient pressure, ie the zero position of the diaphragm does not depend on, for example, variations in atmospheric pressure.
A further advantage of the vent is a flat diaphragm. If the height of the pump chamber is zero, the maximum compression ratio is achieved. However, a certain pump chamber height is required, otherwise the flow resistance within the pump chamber would be very high.
The advantage of the vent is that the pressure on the diaphragm is always in equilibrium, atmospheric pressure does not change the zero position of the diaphragm, high compression ratios can be achieved by the flat diaphragm, and there is no back pressure in the electrode chamber when the diaphragm moves. including the fact that it does not occur.
However, the use of vents may lead to a risk of contamination during manufacturing, processing, sawing, and/or operation. Contamination can appear in the form of particle transport or bellows particle transport, or in the form of condensed moisture. Figure 18 shows the design measures applied to avoid the drawbacks of vents. The design measures applied in FIG. 18 may be applied individually or in combination.

Figure 18a shows a schematic top view of a vent with a capillary stop. The electrode chamber 1810 is connected to the environment via a vent 1890, which includes a capillary stop 1820 in combination with a buffer volume 1860.
The measures of Figures 18b and 18c increase the flow resistance of the vent 1890 so that no significant airflow can flow through the vent and draw in particles during the stroke time when the diaphragm moves. The stroke time may be between 1 ms and 100 ms depending on the pump design and the viscosity of the medium.
Figure 18b shows a schematic top view of the vent with reduced cross section. Flow resistance is increased primarily by reducing the cross section 1840 of the vent.
Figure 18c shows a schematic top view of a vent with a serpentine section. Flow resistance is increased by increasing the ventilation distance and applying serpentine sections 1830.
FIG. 18d shows a schematic top view of a vent 1890 with a filter. A lateral filter 1850 is provided at the vent 1890 and may be one of the simplest measures against particles.
FIG. 18e shows a schematic top view of a vent or electrode chamber 1810 having a buffer volume 1860 that is significantly larger than the stroke volume, for example having four buffer volumes. In this case, there is no direct volume exchange with the environment, only ambient air enters the buffer volume 1860. The buffer volume can be achieved by deep etching in the counter electrode or non-moving electrode structure.

It is also possible to combine the structures described in FIG. These structures may also be realized laterally by dry etching vents facing perpendicularly to the micropump layer. Holes perpendicular to the layer can be covered with foil, but side holes can be contaminated by the sawing and dicing process.
For example, a vent with a diameter of 1 μm would have capillary stops extending between them, possibly significantly reducing the risk of contamination. At the same time, a narrow hole, for example 1 μm in diameter, prevents particles larger than 1 μm from entering the electrode chamber. The main advantages of vents are obtained, such as a flat diaphragm, high compression ratio, and the option of atmospheric pressure compensation.
Additionally, if the pumping frequency is high enough, the overpressure that builds up in the electrode chamber during high-speed travel can be used to increase the backpressure capability of the micropump.

FIG. 19 shows a schematic side view of a micropump similar to that of FIG. 2 with a pre-deflected diaphragm 1910 in an inoperative state as shown in FIG. 19a and in an activated state as shown in FIG. 19b.
In FIG. 19a, the distance between pre-deflected diaphragm 1910 and stator structure 1920 is minimal in the central region of the electrode chamber. In some cases, pre-deflected diaphragm 1910 may contact stator structure 1920. Stator structure 1920 does not include vents. Deflection of diaphragm 1910 is caused by negative pressure during wafer bonding. The vacuum during wafer bonding, along with the plate stiffness of diaphragm 1910, can be used to adjust the rate of deflection of diaphragm 1910 in a defined manner. Although pre-deflection can be generated by judicious selection of the pressure ratio between the electrode chamber pressure and atmospheric pressure, as well as the selection of the surface and thickness of the diaphragm, contact can only be established by actuating the diaphragm. It is important to keep this in mind. In this case, the operating voltage is slightly higher but the stroke volume is slightly larger compared to a micropump in which the pre-deflected diaphragm contacts the stator structure in the inactive state.

This offers the advantage that vents are not required, i.e. to suck air in and out during processing where slurry etc. from polishing are present, during dicing where sawdust etc. enter through capillary forces. This means that there is no risk of particle contamination during operation in air with no bellows particles, and also under special operating conditions such as water droplets penetrating the vents.
A further advantage of pre-deflecting diaphragm 1910 with negative pressure during wafer bonding is a curved bend line. The curved bend line forms a geometric wedge 1940 with the cross-sectionally flat stator structure, creating a moving wedge effect and reducing the drive voltage.

As shown in FIG. 19b, when the micropump is actuated, the diaphragm 1910 is drawn towards the stator structure 1920, so that the diaphragm device 1910 contacts the stator structure 1920 in the central region and the wedge 1940 move towards the surrounding area.
While planning or designing a pre-deflected diaphragm, it must be taken into account that a diaphragm that has been pre-deflected by the use of vacuum or low pressure is deflected so strongly that it leaves the hook region of the plate theory and becomes more rigid. It won't happen.
Vacuum or pressure during the bonding process can be used to adjust the pre-deflection and, if desired, the shape of the electrode chamber can be adjusted by the plate stiffness of the diaphragm.

FIG. 20 shows the known electrostatic micropump 2000 of Zengerle et al. with a silicon diaphragm having a thickness of, for example, 40 μm and a side length of, for example, 5 mm. This micropump can overcome back pressures of approximately 30 kPa, which corresponds to 0.3 bar, in incompressible fluids such as water. If its diaphragm is preloaded with a vacuum, the electrode chamber requires significantly more space.
In Zengerle pumps, the distance between the diaphragm layer and the stator structure is, for example, 5 μm. The disadvantages of the Zengerle pump are its low capacity, eg only 40 nl, the need for high voltages, eg at least 200 volts, and the use of a ventilation chamber.
Advantages of the moving wedge include lower voltage requirements due to the higher electric field strength in the wedge region and greater volume stroke by winding the moving wedge. The disadvantage is that the stroke volume is smaller than without the pre-deflected diaphragm.
Adjustment of negative pressure during wafer bonding allows other configurations of structures. The zero distance of the pre-deflected diaphragm can be adjusted by negative pressure and electrode chamber design. This makes it possible to realize a mixed configuration of a moving wedge pump and a normal pump.

The known micropump 2000 differs in manufacture and function from the current application.
First, the diaphragm deflection of layer 3 and insulating layer 8 of the known micropump occurs within the electrode or actuator chamber 10 towards layer 2 and away from pump chamber 90 .
A further difference is that the electrical insulation of the known micropump is provided by an insulating layer 8 and an electrical feedthrough protective spacer 9.
A further difference is that sidewall insulation of known micropumps is impractical as sawing and/or dicing destroys the sidewall insulation and is only possible by processing the individual pieces one by one after dicing. .
Moreover, there is no adjustment of the distance between the electrode structures to reduce the supply voltage. Anti-stiction bumps are also absent from known micropumps.

Implementation Alternatives Although some aspects have been described in the context of an apparatus, it will be clear that these aspects also represent corresponding method descriptions, where the blocks or devices correspond to method steps or features of method steps. Similarly, aspects described in the context of method steps also represent a description of corresponding blocks or items or features of the corresponding apparatus.

Regarding bump design, there are the following boundary conditions. The height of the bump should be as small as possible since it reduces the stroke of the actuator. Regarding etching techniques, heights of 10 nanometers to 200 nanometers are achievable. Small gaps are sufficient to avoid charge relaxation in these regions.
The contact area of all bumps should be much smaller compared to the contact area without bumps (to reduce sticking). However, if the total contact area of all bumps is too small, the entire force will be concentrated on this small area and may exceed the mechanical stability of the bumps. Electrostatic compressive forces on the bumps can cause damage to the bumps. For this purpose, this contact area should be selected to be significantly below the maximum mechanical stress that can be applied. For single crystal silicon, this value is approximately 4 GPa, and for silicon oxide it is a smaller value.

By activating the electrostatic drive of the micropump 100, the diaphragm device 180 is drawn toward the valve device 120 while compressing the pump chamber 110. Compression of the pump chamber 110 increases the pressure within the pump chamber 110 and opens the valve flap 140 of the outlet check valve 170, allowing fluid to exit the pump chamber 110 through the outlet check valve 170 and into the environment. .
Reducing the voltage between the first electrode structure 109 and the second electrode structure 108 causes the diaphragm device 180 to move towards its initial or zero position, while expanding the pump chamber 110. You can move back inside. Expansion of pump chamber 110 causes valve flap 140 of inlet check valve 160 to open, allowing fluid to flow from the environment through inlet check valve 160 and into pump chamber 110 . At the same time, by blocking fluid flow through the outlet tunnel 150 with the valve flap 140, the check valve 170 may block fluid flow through the outlet tunnel.

The electrostatic micropump 100 of FIG. 1 has several advantages compared to prior art micropumps. The stepped variable height configuration 107 of the pump chamber 110 may operate with a low supply voltage compared to that of prior art micropumps. This low supply voltage, although still within the high voltage range, is considered low compared to the supply voltage of prior art micropumps. This lower supply voltage reduces the energy usage of electrostatic micropump 100 and allows the use of compact, well-established high voltage circuits.
As a further advantage, operating electrostatic micropump 100 may overcome some backpressure. The back pressure prevents movement of the diaphragm device 180. Increasing the supply voltage increases the static voltage that overcomes the back pressure.
Electrostatic micropumps 100 for non-conductive fluids such as air have a high compression ratio, which can be higher than electrostatic micropumps for conductive fluids such as micropump 200 of FIG. This is because the deflection of diaphragm device 180 points toward pump chamber 110 and may reduce additional dead volume 106.

FIG. 7 shows an insulating oxide layer 610 over the variable height feature 560 of the etched second layer 302, according to one embodiment for manufacturing an electrostatic micropump, such as the electrostatic micropump 200 of FIG. FIG. 3 shows a schematic side view of an insulated second layer 302 with anti-stiction bumps 708 that can be obtained by etching anti-stiction bumps 708. FIG.
FIG. 7 further shows a top view of an etch mask 710 configured to be used to etch anti-stiction bumps 708. The etch mask 710 used to etch the anti-stiction bump 708 comprises a circular shape 720 with a dot pattern 730.
The anti-stiction bumps 708 are etched by a dry or wet etching process using KOH to a very small target depth (e.g. between 20 nm and 200 nm; the target diameter of the anti-stiction bumps 708 is e.g. 20 μm). It's okay. Anti-stiction bump 708 is similar to anti-stiction bump 208 of FIG.

FIG. 10 shows a schematic side view of an actuator device that can be obtained by removing the insulating layer 610 from the main surface of the actuator device 920 , according to an embodiment for manufacturing a micropump, such as the micropump 200 of FIG. .
Removal of the oxide layer may be performed by a wet chemical process such as HF-Dip. By removing the insulating layer on the main surface of the actuator device 920, electrical contact can be made with the first layer and/or the second layer 301, 302.

FIG. 11 shows a schematic side view of an actuator device 920 that can be obtained when the first layer 301 of the actuator device 920 is thinned, according to an embodiment for manufacturing a micropump, such as the micropump 200 of FIG. . The thickness of the first layer 301 is determined in order to form a diaphragm from the first layer 301, i.e. to make the layer 301 deflectable and mechanically stable enough to avoid breakage when deflected. decrease the For example, the first layer 301 may be as thin as, for example, 750 μm to, for example, 30 μm.
For example, the thinning process may be performed by grinding the first layer 301 from 750 μm to 100 μm and then applying chemical mechanical polishing (CMP) to reach a thickness of, for example, 50 μm. The remaining 20 μm, for example, can be etched away by dry etching. The first layer 301 is a diaphragm having a thickness in the same range as the diaphragm device 230 of FIG.
If the diaphragm formed from the first layer 301 is a non-conductive diaphragm, deposition of an electrode structure on the diaphragm is recommended.

The known micropump 2000 differs in manufacture and function from the current application.
Firstly, a deflection of the diaphragm of the layer 3 and the insulating layer 8 of the known micropump occurs within the electrode or actuator chamber 10 towards the layer 2 and away from the pump chamber 19 .
A further difference is that the electrical insulation of the known micropump is provided by an insulating layer 8 and an electrical feedthrough protective spacer 9.
A further difference is that sidewall insulation of known micropumps is impractical as sawing and/or dicing destroys the sidewall insulation and is only possible by processing the individual pieces one by one after dicing. .
Moreover, there is no adjustment of the distance between the electrode structures to reduce the supply voltage. Anti-stiction bumps are also absent from known micropumps.

Claims (37)

An electrostatic micropump,
a diaphragm device comprising a diaphragm and a first electrode structure;
A valve device comprising an inlet check valve and an outlet check valve,
a valve device, wherein the diaphragm device and the valve device at least partially surround a pump chamber;
a second electrode structure arranged to form an electrostatic drive section with the first electrode structure, the second electrode configured such that the electrostatic drive section deflects the diaphragm; structure and
at least one anti-stiction bump disposed between the first electrode structure and the second electrode structure;
in an inoperative state of the micropump, the spacing between the first electrode structure and the second electrode structure varies from a peripheral region of the pump chamber toward a central region of the pump chamber; An electrostatic micropump, wherein the peripheral region surrounds the central region. the first electrode structure and/or the second electrode structure having a variable height configuration, the spacing between the first electrode structure and the second electrode structure being adjusted to The electrostatic micropump according to claim 1, wherein the electrostatic micropump increases from the peripheral region toward the central region. 3. An electrostatic micropump according to any one of claims 1 or 2, wherein the at least one anti-stiction bump is arranged on the second electrode structure opposite the variable height feature. From claim 1, wherein the spacing between the first electrode structure and the second electrode structure increases stepwise in a plurality of steps from the peripheral region towards the central region of the pump chamber. 3. The electrostatic micropump according to any one of 3. providing mechanical contact to the first electrode structure and the second electrode structure in the peripheral region; and providing electrical penetration between the first electrode structure and the second electrode structure. The electrostatic micropump according to any one of claims 1 to 4, wherein the first electrode structure and the second electrode structure are insulated from each other by an insulating layer that prevents the occurrence of. The electrostatic drive unit is configured to change the pressure in the pump chamber and/or the volume of the pump chamber based on the voltage between the first electrode structure and the second electrode structure. The electrostatic micropump according to any one of claims 1 to 5, wherein the electrostatic micropump is the valve device is a layer device;
the inlet check valve and the outlet check valve are arranged in-plane with respect to the valve arrangement;
Both the inlet check valve and the outlet check valve include an inlet tunnel, a valve flap, an outlet tunnel, and a dead volume passing through the inlet tunnel, the valve flap in an open state, and the outlet tunnel. from claim 1, wherein the fluid flow direction through the inlet check valve is opposite to the direction of the fluid flow through the outlet check valve. 6. The electrostatic micropump according to any one of 6. 8. An electrostatic micropump according to any preceding claim, wherein the diaphragm device comprises a conductive layer that is at least part of the first electrode structure. the valve device comprises a stack of semiconductor layers and has a thickness of 480 μm to 540 μm perpendicular to a major surface of the valve device;
Electrostatic micropump according to any one of claims 1 to 8, wherein and/or the diaphragm device comprises a semiconductor layer with a thickness of 10 μm to 120 μm perpendicular to the main surface of the valve device. 10. An electrostatic micropump according to any one of claims 1 to 9, wherein the valve device comprises a conductive layer that is at least part of the second electrode structure. The electrostatic drive is configured to, when actuated, deflect the diaphragm toward the valve arrangement to compress the pump chamber and cause fluid to flow from the pump chamber through the outlet check valve. The electrostatic micropump according to claim 10. 12. The electrostatic micropump of claim 11, wherein the fluid flowing from the pump chamber through the outlet check valve is a non-conductive fluid. the valve device comprises a stack of silicon layers and has a thickness of 480 μm to 540 μm perpendicular to the main surface of the valve device;
Electrostatic micropump according to any one of claims 10 to 12, wherein and/or the diaphragm device comprises a silicon layer with a thickness of 10 μm to 120 μm perpendicular to the main surface of the valve device. a stator structure, the diaphragm device being disposed between the valve structure and the stator structure, the stator structure and the diaphragm device surrounding an electrode chamber; 10. An electrostatic micropump according to any preceding claim, comprising a stator structure comprising a conductive layer which is at least part of the second electrode structure. The electrostatic drive, when actuated, deflects the diaphragm device toward the stator structure to expand the pump chamber so that fluid flows through the inlet check valve and into the pump chamber. The electrostatic micropump according to claim 14, configured to. 16. The electrostatic micropump of claim 15, wherein the fluid flowing into the pump chamber through the inlet check valve is an electrically conductive or non-conductive fluid. 17. Electrostatic micropump according to any one of claims 14 to 16, wherein the stator structure comprises a silicon layer and has a thickness of 450 μm perpendicular to the main surface of the valve arrangement. 18. An electrostatic micropump according to any one of claims 14 to 17, wherein the stator structure has a higher stiffness compared to the diaphragm device. 19. An electrostatic micropump according to any one of claims 14 to 18, wherein the electrostatic micropump comprises a vent configured to connect the electrode chamber with the environment of the electrostatic micropump. 20. The electrostatic micropump of claim 19, wherein the vent is configured to prevent contamination of the electrode chamber. 21. Electrostatic micropump according to claim 19 or 20, wherein the vent comprises a filter and/or buffer volume configured to prevent contamination of the electrode chamber. 22. Electrostatic micropump according to any one of claims 14 to 21, wherein the diaphragm of the diaphragm device is pre-deflected. The diaphragm device is pre-deflected to form mechanical contact with the stator structure in a contact area in the non-actuated state of the electrostatic drive, and the diaphragm device is pre-deflected to form mechanical contact with the stator structure in the contact area in the non-actuated state of the electrostatic drive; 23. An electrostatic micropump according to claim 22, adapted to increase area. the conductive layer of the first electrode structure and the conductive layer of the second electrode structure are made of a conductive material or a highly doped semiconductor material having the conductivity of a metallic material; An electrostatic micropump according to any one of claims 1 to 23. A process for manufacturing an electrostatic micropump, the process comprising:
arranging a diaphragm device to include a diaphragm and a first electrode structure;
arranging a valve arrangement to include an inlet check valve and an outlet check valve, the step comprising:
the diaphragm device and the valve device at least partially surrounding a pump chamber;
arranging a second electrode structure so as to form an electrostatic drive with the first electrode structure to deflect the diaphragm;
disposing at least one anti-stiction bump between the first electrode structure and the second electrode structure;
in an inoperative state of the micropump, the spacing between the first electrode structure and the second electrode structure varies from a peripheral region of the pump chamber toward a central region of the pump chamber; A process for manufacturing an electrostatic micropump, wherein the peripheral region surrounds the central region. arranging the diaphragm device,
disposing the first layer, the first layer having a variable height shape and an insulating groove on a first major surface of the first layer;
forming an insulating layer on a first major surface of the first layer to position the diaphragm device. arranging the diaphragm device,
providing a second layer;
The first major surface of the first layer is attached to the first major surface of the second layer so that the variable height shape of the first layer and the first major surface of the second layer forming an electrode chamber between the main surface;
thinning the second major surface of the second layer parallel to the first major surface in order to position the diaphragm device, at least in a region opposite the electrode chamber; 27. A process for manufacturing an electrostatic micropump according to claim 26. The step of creating a variable height feature on a first major surface of the first layer includes arranging at least one vent in the first layer, the vent opening extending into the electrode chamber. 28. A process for manufacturing an electrostatic micropump according to claim 27, comprising the further step of bringing the electrostatic micropump into contact with the environment of the electrostatic micropump. 29. The electrostatic micropump of claim 28, wherein the step of locating at least one vent in the first layer comprises the further step of locating at least one filter and/or buffer volume in the vent. The process of manufacturing. arranging the valve device,
forming a first substrate with a first groove structure on a first major surface of the first substrate;
forming a second substrate with a second groove structure on a first major surface of the second substrate;
providing a stack of substrates by attaching the first major surface having a groove structure of the first substrate to the first major surface having a groove structure of the second substrate;
a first and/or a second groove structure forming at least one cavity within the stack of substrates;
thinning the first major surface and/or the second major surface of the stack of substrates;
recessing the stack of substrates in the at least one cavity from a first major surface and a second major surface parallel to the first major surface to form an inlet tunnel and an outlet tunnel and a valve flap therebetween; , configured to direct fluid flow through the inlet tunnel, the valve flap in an open state, and the outlet tunnel;
to produce the valve device, the direction of fluid flow through the inlet check valve is opposite to the direction of fluid flow through the outlet check valve; 30. A process for manufacturing an electrostatic micropump according to any one of claims 25 to 29, comprising manufacturing a valve. 31. A stationary station according to any one of claims 25 to 30, wherein arranging the second electrode structure comprises performing a wafer bonding process or performing a deposition process to deposit an electrode material or an insulator material. The process of manufacturing electric micropumps. disposing at least one anti-stiction bump;
on the second main surface of the first layer parallel to the first main surface, and/or on the first main surface and/or the second main surface of the second layer parallel to the first main surface and/or on the main surface of the valve device facing the diaphragm device,
32. A process for manufacturing an electrostatic micropump according to any one of claims 25 to 31, comprising forming the at least one anti-stiction bump in the region of the pump chamber. attaching the diaphragm device to the valve device such that the diaphragm device and the valve device form a pump chamber;
dicing the first layer in the insulating groove;
depositing a conductive layer on the second major surface of the first layer of the diaphragm device, and on the first major surface of the second layer of the diaphragm device, or on the surface of the valve device; the step of
and dicing the second layer to produce a micropump. 34. Thinning the second major surface of the first layer of the diaphragm device prior to depositing a conductive layer on the second major surface of the first layer. The process of manufacturing electrostatic micropumps. the step of attaching the diaphragm device to the valve device;
pre-deflecting the diaphragm device disposed by the second layer;
35. A process for manufacturing a micropump according to claims 27 to 34, comprising the step of attaching the diaphragm device to the valve device. the step of attaching the diaphragm device to the valve device;
pre-deflecting the diaphragm device arranged by the second layer so as to form a mechanical contact of the first layer in the contact area in the non-actuated state of the electrostatic drive; the electrostatic drive is adapted to increase the contact area in an actuated state;
36. A process for manufacturing a micropump according to claims 27 to 35, comprising the step of attaching the diaphragm device to the valve device. the conductive layer of the first electrode structure and the conductive layer of the second electrode structure are made of a conductive material or a highly doped semiconductor material having the conductivity of a metallic material; A process for manufacturing a micropump according to claims 25-36.

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